P-channel MOSFET switching

dl324

Joined Mar 30, 2015
9,146
No I'm not really geared up for dealing with electronics to be honest. Is there any diy method of preventing static damage? I had read warnings about damaging MOSFETs all right but it was actually the NPN that was the problem.
Basically:
  • Don't handle static sensitive parts by their leads.
  • Wear a grounded grounding strap or, minimally, ground yourself before touching components.
  • Use a conductive work surface
  • Store/transport devices in approved containers
Bipolar devices and diodes aren't static sensitive; but I have some white LEDs that state they are. Don't do something crazy like walk around on carpets with sensitive parts in your hand...

Static can be generated from unexpected sources. Try removing some cellophane tape from it's roll in the dark.
 

Thread Starter

sean1553

Joined Oct 27, 2015
11
Basically:
  • Don't handle static sensitive parts by their leads.
  • Wear a grounded grounding strap or, minimally, ground yourself before touching components.
  • Use a conductive work surface
  • Store/transport devices in approved containers
Bipolar devices and diodes aren't static sensitive; but I have some white LEDs that state they are. Don't do something crazy like walk around on carpets with sensitive parts in your hand...

Static can be generated from unexpected sources. Try removing some cellophane tape from it's roll in the dark.
I'll have to order one of those grounding straps next time I'm buying components. I don't want to be spending hours looking for a problem like I was with this circuit all week!

I've been searching for the correct way to mount/solder the mosfet in my circuit but haven't found much. I will use an arduino prototype shield for the majority of the circuit but the drain and source wires will obviously be a heavier gauge than the rest of the circuit. Do I crimp terminals to the wires and connect straight to the mosfet or is there a better way of doing this? I will also be adding a p600 diode to protect the mosfet and I don't think this will fit the sheild either. I haven't ordered that yet though, so I could be wrong.
 

dl324

Joined Mar 30, 2015
9,146
I will use an arduino prototype shield for the majority of the circuit but the drain and source wires will obviously be a heavier gauge than the rest of the circuit. Do I crimp terminals to the wires and connect straight to the mosfet or is there a better way of doing this?
I'd solder it to the board and run your hefty wires (like 4 #22 wires) to male headers and use mating connectors to connect to the load. You run less risk of shorting something.
I will also be adding a p600 diode to protect the mosfet and I don't think this will fit the sheild either.
If you're not driving an inductive load, you don't need additional protection. With an inductor, a 1N400x type diode would be sufficient.
 

Thread Starter

sean1553

Joined Oct 27, 2015
11
The load is the primary coil of an ignition system so I think I need the diode. It was a p600 that was used in the project I'm going off. I'm not quiet sure why they used such heavy duty components. My mosfet is for 100v and the leads won't fit the holes in a breadboard or perforated board which makes things a bit awkward.

A capacitor was also used in parallel with the diode but I can't figure out why that would be needed. I'm thinking maybe all this is because the service manual for the bike states that primary coil voltage should be 100v. I don't see how that's possible though. As far as I know its just a continuous 12-14v feed from the battery. I'll have to measure it before I go any further...
 

shortbus

Joined Sep 30, 2009
7,080
A capacitor was also used in parallel with the diode but I can't figure out why that would be needed. I'm thinking maybe all this is because the service manual for the bike states that primary coil voltage should be 100v. I don't see how that's possible though. As far as I know its just a continuous 12-14v feed from the battery. I'll have to measure it before I go any further...
The cap will store the high voltage on the primary to help with the next firing of the coil. There is ~400V on the primary when the engine is running. This is due to the collapse of the secondary voltage in the coil when it fires. So your 100V mosfet may get fried when it is trying to run.
 
Top